Temperature Controlled Rate Studies of Co(salen)

Reversible Oxygen BindingBy Philip Chuang

Background Information• Co(salen) is Cobalt N,N’-bis (salicylaldehyde)

ethylenediamine • Ability to reversibly bind oxygen discovered by

Tsumaki in 19381

• A square planar dioxygen carrier• Exists in both an Active and Inactive state• Interested in Effect of Temperaturee on Rate in:

– Oxygenation of Inactive Co(Salen) in DMSO

• [(DMSO)Co(Salen)]2 + O2 [(DMSO)Co(Salen)]2O2

– Deoxygenation of Active Co(salen) in CHCl3• Co(Salen)O2

Co(Salen) + O2

Active State vs. Inactive State

• Active State binds Oxygen readily

• Dimeric Form coordinates between Cobalt centers.2

• Binds Oxygen in polar aprotic solvents

• Dimeric Form coordinates Co and O.3

Diagram from Reference 3Diagram from Reference 2

Hypothesis

• The Rate of Oxygen Binding and Dissociation increases with Higher Temp. More specifically:– The Rate of Inactive Co(salen) Oxygenation

will Increase with Temperature in DMSO.– Rate of Active Co(salen) Deoxygenation will

Increase with Temperature in chloroform.

Synthetic Method• Synthesis of Inactive Co(salen)

– 1 eq. ethylenediamine added to 2 eq. Salicylaldehyde in boiling ethanol, for 4 min.

– 1 eq. Salen product (from above) refluxed in ethanol under Argon, 1 eq. Cobalt Acetate in H2O added via addition funnel

– Stirred and kept in 700C Water bath for 1 hour

• Synthesis of Active Co(salen)– Same methods as Inactive, but no hot water

bath

Procedure derived from Reference 4

UV-Vis

UV-VIS of Inactive Co(salen) in DMSO in atmosphere

UV-Vis of Inactive Co(salen) in DMSO in N2 from literature5

The UV spectra indicates that the Inactive product was obtained.

Differences between UV spectra likely due to availability of Oxygen in the DMSO solution

H-NMR

H-NMR of Active Product in dDMSO

H-NMR of Inactive Product in dDMSO

-The H-NMRs did not correspond to predicted H-NMRs

-Conclusive Identification from H-NMR unobtainable

-Future improvement: prepare H-NMR in inert atmosphere, include C13 NMR

IR Spectra

IR Spectra of inactive Co(salen) from Unniversity of Wimona6

IR spectra of Inactive Co(salen)

With the exception of the C-H peak at 3000, and the nujol peaks at 1500, 1400 and 700 cm-1 look similar

Further reinforces likelihood of obtaining Inactive Product

UV-Vis Kinetics Results pt.1Absorbance vs Time at 15 C, CHCl3, 409 nm

Trace

0.000000

0.020000

0.040000

0.060000

0.080000

0.100000

0.120000

0 100 200 300 400 500 600 700

Time (s)

Ab

sorb

ance

(A

U)

Absorbance vs Time at 15 C, CHCl3, 409 nm Trace

y = -7E-06x + 0.0671

R2 = 0.5286

0.0625000.0630000.0635000.0640000.0645000.0650000.0655000.0660000.0665000.0670000.067500

0 100 200 300 400 500 600 700

Time (s)

Ab

sorb

ance

(A

U)

Absorbance vs Time graph of oxygenated Co(salen) in CHCl3 at 150C

Absorbance vs. Time graph of oxygenated Co(salen in CHCl3 at 150C, excluding first 8 data points

The first 8 data points were removed

Not enough time given to allow temperature to equilibrate

UV-Vis Kinetics Results pt. 2Absorbance vs Time, 50 C, CHCl3, 409 nm Trace

0.000000

0.020000

0.040000

0.060000

0.080000

0.100000

0 200 400 600 800

Time (s)

Ab

so

rba

nc

e (

AU

)

Absorbance vs Time, 50 C, CHCl3, 409 nm Tracey = 2E-05x + 0.0456

R2 = 0.9616

0.046000

0.048000

0.050000

0.052000

0.054000

0.056000

0 200 400 600 800

Time (s)

Ab

so

rban

ce (

AU

)

Absorbance vs. Time graph of oxygenated Co(salen) in CHCl3 at 500C

Absorbance vs. Time graph of oxygenated Co(salen) in CHCl3 at 500C without first 8 data points

Again, the first 8 data points were discarded.

Not enough time was given for temperature to equilibrate

UV-Vis Spectra Results pt. 3-LN Absorbance vs Time, 15 C, 409 nm Time

Trace in CHCl3y = 0.0002x + 2.6812

R2 = 0.629

2.6400002.6600002.6800002.7000002.7200002.7400002.7600002.780000

4.5 104.5 204.5 304.5 404.5 504.5 604.5 704.5

Time

-LN

Ab

sorb

ance

-LN Absorbance vs Time, 50 C, 409 nm Trace, in CHCl3

y = -0.0003x + 3.0807

R2 = 0.9467

2.882.9

2.922.942.962.98

33.023.043.06

4.5 204.5 404.5 604.5 804.5

Time

-LN

Ab

so

rba

nc

e

-LN Absorbance vs Time plot for 150C deoxygenation of Inactive Co(salen)

-LN Absorbance vs. Time plot for 500C deoxygenation of Inactive Co(salen)

The slope of the –LN Absorbance vs. Time plot yields the rate constant of a first order reaction.

UV-Vis Kinetics Results pt. 4Absorbance vs Time, 15 C, DMSO, 409 nm

Trace y = -2E-05x + 0.2922

R2 = 0.9792

0.265000

0.270000

0.275000

0.280000

0.285000

0.290000

0.295000

0.300000

0 200 400 600 800 1000

Time (s)

Ab

so

rba

nc

e (

AU

)

-LN Absorbance vs Time, 15 C, DMSO, 409 nm Time Trace y = 0.0498x + 1.1575

R2 = 0.9733

00.20.40.60.8

11.21.41.6

0 2 4 6 8

Time (s)

-LN

Ab

sorb

ance

Absorbance vs. Time plot for Inactive Co(salen) in DMSO at 150C

-LN Absorbance vs. Time plot for Inactive Co(salen) in DMSO at 150C

No Data points were removed

For the DMSO runs, temperature was allowed to equilibrate

UV-Vis Kinetics Results pt. 5Absorbance vs Time, 50 C, DMSO 409 nm

Time Trace

0.1720.1730.1740.1750.1760.1770.1780.179

0.18

0 200 400 600 800

Time (s)

Ab

so

rba

nc

e (

AU

)

Absorbance vs. Time graph of inactive Co(salen) in DMSO at 500C

Result was not workable, rate could not be calculated

Possible explanations in Discussion Section

Discussion• When LN Absorbance vs. LN Time plotted

(not pictured), linearity observed• Indicated a first order reaction:

– R = k[A] -d[A]/dt = k[A]– -d[A]/[A] = k Integrate to get LN [A] = -kt – Thus k = -LN [A] /t

• This method used to attain reaction rates from results

• Decreasing absorbance indicative of oxygen complex formation5

Discussion• k = 0.0002 1/s for oxygenated Active Co(salen)

in CHCl3 at 150C in atmospheric conditions– Validity in question due to low correlation coefficient

• k = -0.0003 1/s for oxygenated Active Co(salen) in CHCl3 at 150C in atmospheric conditions

• k = 0.05 1/s for inactive Co(salen) in DMSO at 150C

• k could not be determined for inactive Co(salen) in DMSO at 500C– Possible Reason: Reaction has finished– Supported by the lower absorbance compared to the 150C

sample.

Conclusions• Data supports hypothesis for increased rate of

Oxygen Dissociation for Oxygenated Co Active Co(salen) at increased temperatures

• Not enough data to support or disprove hypothesis for increased rate of Oxygen uptake in Active form of Co(salen at increased temperatures.

• Future Considerations:– Prepare NMRs and UV-Vis solutions in an inert

glovebox using a sealable cuvette– Take the C13 NMR to better characterize products– Run more samples at different temperatures to give

better overall picture

References

1. T. Tsumaki, Bull. Chem. Soc. Jpn., 13, 252 (1938).

2. Schaefer, W. P., and Marsh, R. E., Acta Crystallogr., B25, 1675 (1969)

3. Bruckner, S.,Calligaris, M., Nardin, G., and Randaccio, L., Acta Crystallogr., B25, 167 (1969)

4. Bailes, R. H., and Calvin, M., J. Amer. Chem. Soc., 69, 1886 (1947)

5. B. Ortiz, and Park, S., Bull. Korean Chem. Soc. 21, 4, (2000)

Acknowledgements

• I’d like to thank Ankur for always being available to help me at all hours of the day

• Simone for being a big help during the lab sessions and being ridiculously funny

• Professor Roth for allowing me to use her temperature controlled UV-Vis and giving us a cool, albeit hard final project that taught us to make use of the journal articles available to us

• Finally my fellow students for being ever supportive and cheery